This invention relates to a numerical control system which enables simultaneous execution of machining work in an automatic operation mode and another task in a manual mode or manual data input mode.
Machine tools capable of being controlled by a numerical control device include multiple-table and multiple-head milling machines. To simplify matters, assume that such a milling machine has two tables and two heads corresponding to the respective tables. When the numerical control device controlling such a machine tool is operating in the automatic operation mode, one head of the machine is being controlled automatically by the numerical control device. This means that the other head cannot be controlled in the manual mode or manual data input mode, referred to hereinafter as the MDI mode. Therefore, when a workpiece placed on the table corresponding to the former head is being machined in the automatic operation mode by the tool mounted on said head, the other table corresponding to the latter head cannot be moved in the manual or MDI mode. Accordingly, when the operator wishes to prepare the other table and head combination for a subsequent machining operation, such as by setting a workpiece on the table or by applying a lubricating oil, he cannot do so because the former table and head combination is under the automatic control of the numerical control device. The preparatory work for the other machining operation must therefore wait until after the completion of machining being performed in the automatic operation mode. This prolongs total machining time and detracts from the efficiency of the system, partially cancelling the advantages of the expensive machine tool of the type described.